1. Field of the Invention
This invention relates to methods and systems for measuring mechanical property of a vascular wall and a method and system for determining health of a vascular structure.
2. Background Art
The following references are referenced herein:
A. J. Bank et al., “In Vivo Human Brachial Artery Elastic Mechanics Effects of Smooth Muscle Relaxation,” 1999; CIRCULATION 100:41-47;
D. H. Bergel, “The Static Elastic Properties of the Arterial Wall,” J. PHYSIOL., 1961; 156:445-457;
C. Bilato et al., “Atherosclerosis and Vascular Biology of Aging,” AGING (Milano) 1996; 8:221-234;
O. Bonnefous et al., “Non Invasive Echographic Techniques for Arterial Wall Characterization,” IEEE ULTRASONIC SYMPOSIUM, 1996:1059-1064;
J. Blacher et al., “Carotidarterial Stiffness as a Predictor of Cardiovascular and All-Cause Mortality in End-Stage Renal Disease,” HYPERTENSION, 1998; 32:570-574;
J. Blacher et al., “Impact of Aortic Stiffness on Survival in End-Stage Renal Disease,” CIRCULATION 1999; 99:2434-2439;
O. Bonnefous et al., “New TDI Developments for Vascular and Cardiac Applications,” IEEE ULTRASONIC SYMPOSIUM, 2000: 1285-1290;
A. Bruel et al., “Changes in Biomechanical Properties, Composition of Collagen and Elastin, and Advanced Glycation Endproducts of the Rat Aorta in Relation to Age,” ATHEROSCLEROSIS 1996; 127:155-165;
D. Buprez et al., “Relationship Between Periventricular or Deep White Matter Lesions and Arterial Elasticity Indices in Very Old People,” AGE AND AGEING, 2001; 30:325-330;
A. Eriksson et al., “Arterial Pulse Wave Velocity with Tissue Doppler Imaging,” ULTRASOUND IN MED. & BIOL., 2002; Vol. 28, No. 5:571-580;
G. Faury, “Function-Structure Relationship of Elastic Arteries in Evolution: From Microfibrils to Elastin and Elastic Fibres,” PATHOL. BIOL., 2001; 49:310-325;
Y. C. Fung, “Biomechanics: Mechanical Properties of Living Tissues,” 2nd Ed., Spring-Verlag, 1993: 321-391;
G. Guerin et al., “Arterial Stiffening and Vascular Calcifications in End-Stage Renal Disease,” NEPHRO DIAL TRANSPLANTATION, 2000; 15:1014-1021;
Hardung V., “Propagation of Pulse Waves in Visco-Elastic Tubing,” AMERICAN PHYSIOLOGICAL SOCIETY, HANDBOOK OF PHYSIOLOGY, Section 2, Circulation, 1962, Vol. 1, eds., Hamilton, W. F. and Dow, P., 107;
D. R. Kaiser et al., “Brachial Artery Elastic Mechanics in Patients with Heart Failure,” 2001; HYPERTENSION 38:1440-1445;
K. Konner et al., “The Arteriovenous Fistula,” J. AM. SOC. NEPHROL., 2003; 14(6): 1669-80;
G. J. Langewouters et al., “The Static Elastic Properties of 45 Human Thoracic and 20 Abdominal Aortas In Vitro and the Parameters of a New Model,” J. BIOMECH., 1984; 17-425-435;
M. A. Lubinski et al., “Speckle Tracking Methods for Ultrasonic Elasticity Imaging Using Short Time Correlation,” IEEE TRANS. ULTRASON., FERROELECT., FREQ. CONTR., 1999, Vol. 46, pp. 82-96;
A. J. Luik et al., “Arterial Compliance in Patients on Long-Treatment-Time Dialysis,” NEPHROL. DIAL TRANSPLANT, 1997; 12:2629-2632;
J. J. Mai et al., “Strain Imaging of Internal Deformation,” ULTRASOUND IN MED. & BIOL., 2002; Vol. 28, Nos. 11/12:1475-1484;
M. Persson et al., “Estimation of Arterial Pulse Wave Velocity With A New Improved Tissue Doppler Method,” PROCEEDING OF THE 23RD ANNUAL EMBS INTERNATIONAL CONFERENCE, 2001:188-191;
H. Taniwaki et al., “Femoral Artery Wall Thickness and Stiffness in Evaluation of Peripheral Vascular Disease in Type 2 Diabetes Mellitus,” ATHEROSCLEROSIS, 2001; 158:207-214; and
S. Timoshenko et al., “Theory of Elasticity,” 3rd Ed., MCGRAW HILL, New York, 1970.
Arterial compliance has been shown to be a strong indicator of vascular disease; cardiovascular disease, peripheral vascular occlusive disease, diabetes, and renal failure. Changes in the ratio of collagen to elastin in the extracellular matrix of the arterial media is believed to be one of the causes of arterial stiffness (Faury 2001; Bilato and Crow 1996; Bruel and Oxlund 1996). By measuring mechanical properties of tissue, elasticity imaging could non-invasively monitor vascular pathologies developing within the vascular wall. Previous attempts at non-invasive vascular elastic imaging include arterial wall motion estimation (Bonnefous et al., 1996; Taniwaki et al., 2001; Luik et al., 1997; Guerin et al., 2000), intraparietal strain imaging (Bonnefous et al., 2000) and pulse wave velocity measurement (Eriksson et al., 2002; Persson et al., 2001). Arterial compliance measurement was also conducted by monitoring internal pulsatile deformation in tissues surrounding the normal brachial artery (Mai and Insanna 2002). With some limits, these measurements have been correlated with clinical events including stroke (Buprez et al., 2001) and claudication symptoms (Taniwaki et al., 2001) in non-ESRD (End Stage Renal Disease) patients and adverse cardiovascular events in patients with ESRD (Blacher et al., 1998; Blacher et al., 1999), as well as length of time on dialysis (Luik et al., 1997).
One factor limiting the success of previously used methods is that arteries normally distended under physiologic pressure produce only small strain. The normal arterial wall, however, is a highly non-linear elastic medium, as illustrated by the solid curve in FIG. 1. The change of arterial elasticity due to intraluminal pressure was previously reported and analyzed over 40 years ago (Bergel 1961). FIG. 1 qualitatively captures the essential feature of nonlinear arterial wall compliance. Under physiologic loading, the mean arterial pressure produces a high effective elastic modulus in the wall. Consequently, the arterial pressure pulse only creates small radial strain (FIG. 1).
Another factor limiting the success of previous methods is that properties of the vessel as a whole or in cross-section are measured. In the previous reports on the arterial compliance over a wide range of intraluminal pressure (Bank et al., 1999; Kaiser et al., 2001), the compliance was inferred from the geometrical changes such as artery diameter and lumen cross-section based on a numerical model (Langewouters' model; Langewouters et al., 1984).
A phase-sensitive, two-dimensional speckle-tracking algorithm has been used by one of the co-inventors herein to determine displacements and strains (Lubinski et al., 1997).